Int 1Ah, 00h            Read System-Timer Time Counter                    all

    Reports the current time of day, and whether 24 hours has passed
    since 1) the last power-on, 2) the last system reset, or 3) the
    last system-timer time read or set.

        Entry   AH = 00h

        Return  CX = High-order part of clock count
                DX = Low-order part of clock count
                AL = 0 if 24 hours has not passed; else 1

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    The following formulas convert the clock count to the time of day:

                Hour      = Clock / 65543 (1007h)
                Remainder = Clock MOD 65543

                Minutes   = Remainder / 1092 (444h)
                Remainder = Remainder MOD 1092

                Second    = Remainder / 18.21
                Remainder = Remainder MOD 18.21

                Hundredths = CINT(Remainder * 100)


    The "system timer" (as distinguished from the real-time clock) is
    the timer that's set when the system is started. This time is
    temporary, lasting only as long as the system is turned on.

    The clock count may also be read as a 4-byte integer at memory
    location 0040h:006Ch. This 4-byte value is equal to the 4-byte
    integer in CX:DX after Service 00h has been called.

    After the call, the flag (at 0040h:0070h) stating whether 24 hours
    has passed or not, is cleared.

    When TIME is typed at the command line, DOS gets the time by means
    of this service.

    Counts occur at the rate of 18.2 per second.